Exosomes derived from human umbilical cord mesenchymal stem cells (hucMSC-Exos) were reported to play a potential role in improving pulmonary fibrosis (158), since they transfer let-7i-5p to inhibit the activation of fibroblasts and then alleviate pulmonary fibrosis through the TGFBR1/Smad3 signaling pathway (159). This evidence concerns the gene SMAD3 and pulmonary fibrosis.